1. Field of the Invention
The present invention relates to a stereoscopic retinal camera, and more particularly to a stereoscopic retinal camera comprising a photographing diaphragm preferable to photograph the eye of a small pupil diameter, and to photograph without using the mydriatica, namely, under non-mydriasis of the pupil.
2. Description of Related Art
Conventionally, simultaneous stereoscopic retinal camera comprises a photographing diaphragm disposed in a position substantially conjugated with the pupil of the examinee's eye, which separates the luminous flux reflected by the fundus of the eye into two luminous flux, and an image forming optical system disposed on each optical path of the two luminous flux to photograph an image of the fundus focused on a photographing film through the image forming optical system by a flashlight. The almost conventional photographing diaphragm are small circle or round in shape.
A photographing diaphragm in the retinal camera is arranged substantially conjugate with the pupil of the examinee's eye, and also there is known from experience that the stereobase being not less than 3 mm may give a satisfactory stereoscopic vision in the stereoscopic retinal observation, the stereobase being a central distance between a right and left diaphragms on a surface of the pupil the satisfactory stereoscopic vision may be obtained in the stereoscopic retinal observation when the stereobase being a central distance between a right and a left diaphragms on a surface of the pupil.
When trying to photograph by such a stereoscopic retinal camera without the mydriasis, one flash for photographing the fundus will make the examinee's eye miosis, then, the sequential photographing can not be continued. Therefore, the condition requested for the non-mydriasis photographing is to photograph certainly by one flash. It is also desired that a pupil diameter capable of being photographed is the shortest possible diameter. However, it is necessary in the stereoscopic photographing that two photographing luminous flux are taken out respectively from right and left sides of the optical axis on the pupil, whereby the shortest pupil diameter necessary to produce the luminous flux will become larger. Thus, non-mydriasis photographing needing the capacity to coordinate with respect to a small pupil diameter is considered unfit for a stereoscopic retinal camera.
For example, when a stereobase on the pupil is 3 mm and a pupil of the a .phi.4 mm diameter, the luminous flux to be transmitted into the pupil can have only 1 mm diameter through the conventional circular diaphragm as shown in FIG. 1, and the light quantities will be 1/2.25 based on that a diameter of luminous flux in a standard retinal camera is about .phi.1.5 mm.
A relation between visual resolution (.psi.) and pupil diameter (d) will be given in accordance with the following formula: sin .psi.=1.22.times..lambda./d, where .lambda. represents a wavelength of luminous flux, and then, .psi. is about 1.77.degree. (.lambda.=550 nm) when d=1, about 1.18.degree. when d=1.5. It is thus understood that the visual resolution (.psi.) lowers by about one-third, so that the vision quantity of the fundus can not be preferably obtained.
As described above, when keeping the stereobase 3 mm and using a small circular diaphragm in the conventional apparatus, it will be necessary to expand the pupil of the examinee's eye correspondingly to heighten the resolving power of photographing by extending the diaphragm, or to introduce much quantity of the light. Thus, if a standard diaphragm diameter of a retinal camera is about .phi.1.5 mm and the stereobase is 3 mm, the pupil needs to have a diameter of 4.5 mm and more, namely, it is not able to photograph the fundus of the eye when the pupil diameter is less than 4.5 mm.
It is said that a stereoscopic retinal camera is very useful in diagnosing a case of glaucoma, particularly the gradual change in progressing condition thereof, but the use of mydriatica is prohibited because the mydriatica causes the deterioration of condition dependent upon the progressing condition. Therefore, the stereoscopic retinal camera has limits of the use also in a case for which the retinal camera is very useful.